|If you want better performance, add more RAM...512MB simply isn't enough these days.|
So what are you showing us? It doesn't appear to be overclocked so are you just showing us the default settings? We need to know the make/model of your motherboard & the type/speed of RAM.
The FX5900XT was the budget card in the FX5900 family. Generally the core clock should run at 400MHz & the RAM at 400MHz (800MHz DDR). Manufacturer's don't have to follow nvidia's reference specs though.